The present invention relates to a device for developing electrostatic charge images produced on the surface of an electrophotographic recording material in a copier which employs a magnet having on its surface a magnetic brush formed of magnetizable toner particles, the copier further presenting a recording material guide path which extends at a distance from the magnetic brush.
In such devices, the sheet-like recording material is brought to the magnetic drum and must be guided so that the developing will be uniform. In some devices the recording material is brought into sliding contact with the magnetic brush, as disclosed, for example, in German Auslegeschrift [Published Application] No. 1,472,997. Guide surfaces in the known arrangement prevent the leading edge of the recording material from entering into the developer, but it is not possible to achieve uniform control of the pressure with which the recording material is pressed against the magnetic brush.
The guide surfaces of this arrangement are formed by curved guide elements which, because they are stiff and unyielding, must be installed accurately. In particular, they must be installed so that the gap between the guide plane and the magnetic brush is set in a precise manner. If this gap is too small, the guide elements may be soiled by contact with developer particles or due to electrostatic attraction of such particles, which particles may then adhere to the back of the recording material and soil it. If the gap is too large, the pressure with which the recording material is pressed against the magnetic brush is insufficient.
This known arrangement does not include any means for adjusting the gap between the recording material and the magnetic brush. Such adjustment may be necessary if different types of toners are employed because the thickness of the magnetic brush which is held by the magnetic drum depends on the magnetizability of the respective toner.